On 07/14/17 13:54, Liu Bo wrote:

On Fri, Jul 14, 2017 at 08:22:31AM -0600, Jens Axboe wrote:

quoted

On 07/14/2017 07:47 AM, Ming Lei wrote:

quoted

quoted

@@ -156,6 +156,9 @@ static inline void *bio_data(struct bio *bio)
 /*
  * drivers should _never_ use the all version - the bio may have been split
  * before it got to the driver and the driver won't own all of it
+ *
+ * Note that cloned bios must not use this as their bi_vcnt may be invalid and
+ * this could lead to silent corruptions.
  */
 #define bio_for_each_segment_all(bvl, bio, i)                          \
        for (i = 0, bvl = (bio)->bi_io_vec; i < (bio)->bi_vcnt; i++, bvl++)
--

2.13.0

Maybe we can add a warning here if it is a cloned bio.

I think that's a good idea, it's easy for people to get this wrong, and
the consequences can be dire. How about something like this?

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7b1cf4ba0902..13b6ac6eae29 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h

@@ -155,9 +155,12 @@ static inline void *bio_data(struct bio *bio)
 
 /*
  * drivers should _never_ use the all version - the bio may have been split
- * before it got to the driver and the driver won't own all of it
+ * before it got to the driver and the driver won't own all of it.
+ *
+ * Don't use this on cloned bio's.
  */
 #define bio_for_each_segment_all(bvl, bio, i)				\
+	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));			\
 	for (i = 0, bvl = (bio)->bi_io_vec; i < (bio)->bi_vcnt; i++, bvl++)
 
 static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,

This patch gave me a crash, I'm double checking it..

thanks,
-liubo

[  104.140220] BUG: unable to handle kernel paging request at ffffffffa0399c1a
[  104.140675] IP: report_bug+0xc4/0x180
[  104.140916] PGD 2626067 
[  104.140917] P4D 2626067 
[  104.141089] PUD 2627063 
[  104.141259] PMD 2346aa067 
[  104.141429] PTE 800000023569c161
[  104.141610] 
[  104.141926] Oops: 0003 [#1] SMP
[  104.142137] Dumping ftrace buffer:
[  104.142366]    (ftrace buffer empty)
[  104.142602] Modules linked in: btrfs(OE) xor raid6_pq ppdev parport_pc parport serio_raw nfsd auth_rpcgss nfs_acl lockd grace sunrpc [last unloaded$
 xor]
[  104.143493] CPU: 0 PID: 144 Comm: kworker/u16:4 Tainted: G        W  OE   4.12.0+ #801
[  104.144009] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc25 04/01/2014
[  104.144654] Workqueue: btrfs-rmw btrfs_rmw_helper [btrfs]
[  104.145009] task: ffff8802382f8000 task.stack: ffffc90000f80000
[  104.145393] RIP: 0010:report_bug+0xc4/0x180
[  104.145668] RSP: 0018:ffffc90000f83ac8 EFLAGS: 00010002
[  104.146015] RAX: 0000000000000001 RBX: ffffffffa0356cff RCX: 0000000000000001
[  104.146474] RDX: ffffffffa0399c10 RSI: 0000000000000480 RDI: 0000000000000000
[  104.146931] RBP: ffffc90000f83ae8 R08: 0000000000000907 R09: 0000000000000000
[  104.147393] R10: 000000005170b2af R11: 000000002b881219 R12: ffffc90000f83c38
[  104.147852] R13: ffffffffa038a415 R14: 0000000000000004 R15: 0000000000000006
[  104.148315] FS:  0000000000000000(0000) GS:ffff88023a600000(0000) knlGS:0000000000000000
[  104.148836] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  104.149211] CR2: ffffffffa0399c1a CR3: 00000002244fc000 CR4: 00000000000006f0
[  104.149672] Call Trace:
[  104.149840]  fixup_bug+0x43/0x60
[  104.150060]  do_trap+0x18a/0x1f0
[  104.150276]  do_error_trap+0xdf/0x1a0
[  104.150606]  ? index_rbio_pages+0x14f/0x160 [btrfs]
[  104.150929]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[  104.151241]  do_invalid_op+0x20/0x30
[  104.151478]  invalid_op+0x1e/0x30
[  104.151787] RIP: 0010:index_rbio_pages+0x14f/0x160 [btrfs]
[  104.152148] RSP: 0018:ffffc90000f83ce8 EFLAGS: 00010002
[  104.152488] RAX: ffffffffa0421938 RBX: 0000000000000000 RCX: 0000000000000000
[  104.152947] RDX: 0000000000000003 RSI: 0000000000000001 RDI: ffffffffa0440420
[  104.153410] RBP: ffffc90000f83d18 R08: 0000000000000000 R09: 0000000000000000
[  104.153869] R10: 0000000000000001 R11: 000000002b881219 R12: ffffffffa0421960
[  104.154330] R13: 0000000000000001 R14: ffff880236e00000 R15: ffff880227718080
[  104.154882]  ? index_rbio_pages+0xc6/0x160 [btrfs]
[  104.155286]  rmw_work+0x76/0x310 [btrfs]
[  104.155633]  btrfs_scrubparity_helper+0xad/0x8e0 [btrfs]
[  104.156070]  btrfs_rmw_helper+0xe/0x10 [btrfs]
[  104.156364]  process_one_work+0x34f/0x9c0
[  104.156631]  worker_thread+0x34a/0x6b0
[  104.156879]  kthread+0x180/0x190
[  104.157095]  ? create_worker+0x230/0x230
[  104.157352]  ? kthread_create_on_node+0x70/0x70
[  104.157648]  ? kthread_create_on_node+0x70/0x70
[  104.157944]  ret_from_fork+0x2a/0x40
[  104.159436] RIP: report_bug+0xc4/0x180 RSP: ffffc90000f83ac8
[  104.159803] CR2: ffffffffa0399c1a
[  104.160026] ---[ end trace 78686c1f7150bacf ]---

(+Peter)
 
Hello Peter,

In a test I ran myself with kernel v4.12-rc1 I also noticed that a
WARN_ON_ONCE() statement triggered an oops in report_bug() and killed the
kernel thread of the caller instead of letting the caller continue. What I
ran into is probably the same oops as in the above call trace. For the test
I ran myself the disassembly is as follows:

(gdb) list *(report_bug+0x94)
0xffffffff812ba024 is in report_bug (lib/bug.c:177).
172                                     return BUG_TRAP_TYPE_WARN;
173
174                             /*
175                              * Since this is the only store, concurrency is not an issue.
176                              */
177                             bug->flags |= BUGFLAG_DONE;
178                     }
179             }
180
181             if (warning) {

Could this be related to patch "debug: Add _ONCE() logic to report_bug()"?
Is this a known issue? If so, is a fix perhaps already available?

Thanks,

Bart.